Recently the solid oxide fuel cell (SOFC) has been a promising means of converting chemical energy into electrical energy by an electro-chemical mechanism. Usually in the conventional SOFC, the Yttria Stabilized Zirconia (YSZ) is used as the electrolyte, the cermet composed of nickel (Ni) and YSZ is used as the anode, and the perovskite composed of LaMnO3 is used as the cathode.
When the SOFC works in a high-temperature environment, the anode fuel, H2, may somehow be suddenly interrupted, such that the air may get into the anode of the fuel cell. Since Ni, the metal catalyst for fuels will be oxidized and have its volume increased and its expansion coefficient changed, the anode of the SOFC tends to be broken into pieces.
Consequently, La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) has been proposed as another option for the anode material of the SOFC, in which hydrogen (H2) or methane (CH4) can be utilized as the fuel and the redox stability of anode can be improved. However, the catalytic conversion efficiency of LSCM is less than that of Ni, and also LSCM is not a good conductor for oxygen (O) ions. Various anode materials have been developed for the SOFC, such as an anode composed of mixed LSCM and YSZ (LSCM-YSZ) or mixed LSCM and Gd-doped ceria (LSCM-GDC). Furthermore, some metal catalyst, such as palladium (Pd), rhodium (Rh), copper (Cu) or Ni, can be doped into this kind of LSCM-YSZ or LSCM-GDC anode to improve the catalytic ability of the anode. In a prior art disclosed in U.S. Pat. No. 7,504,172, a slurry layer is screen-printed on the YSZ electrolyte layer to form a LSCM anode. Also a layer of Ce0.8Gd0.2O2 (GDC) is added between the YSZ electrolyte layer and the LSCM anode to decrease polarization resistance of the anode. It is in need that the polarization resistances of above mentioned anodes are further reduced with improving the anode redox stabilities of SOFC cells.
Moreover, to increase the anode redox stability of a solid oxide fuel cell, it is disclosed that another nickel oxide (NiO) acting as oxidation barrier layer (Journal of The Electrochemical Society, 153(10), A1929, 2006) is coated on the supporting substrate. The NiO particle in this layer has a size less than the NiO particles in the anode, and is to be reduced to a porous Ni layer when the full cell is in the normal operation conditions. This porous fine Ni layer tends to be re-oxidized (or absorbs the leakage oxygen) more easily, so as to absorb abnormal leak oxygen to improve redox stability of the anode of a solid oxide fuel cell. However, the permeability of fuel gas decreases accordingly.